With reference to FIG. 9, a conventional lock structure 10 installed at a door includes a case 11, a first latch 12, a second latch 13 and a third latch 14. The first latch 12, the second latch 13 and the third latch 14 have to be driven respectively by a knob or a door key to lock the door when the door is closed. Similarly, the first latch 12, the second latch 13 and the third latch 14 still have to be driven respectively by the knob or the door key to unlock the door therefore leading to inconvenience of the user.